The invention relates to techniques for making three dimensional objects, and particularly to solid freeform fabrication techniques and objects made through use of such techniques.
Solid Freeform Fabrication (xe2x80x9cSFFxe2x80x9d) or rapid prototyping techniques are typically useful for quickly making complex or simple three dimensional objects. In general, SFF processes enable rapid and accurate fabrication of three dimensional objects which otherwise could be produced only by lengthy molding and machining processes. SFF techniques are, generally speaking, additive processes whereby the object to be formed is fabricated by reducing a model or representation of the object""s ultimate configuration into a series of planar cross-sections and subsequently recompiling the cross-sections to reconstruct the object.
Stereolithography is one of several known SFF techniques. In practicing this process using equipment commonly known as stereolithography apparatus (xe2x80x9cSLAxe2x80x9d), an ultraviolet laser beam selectively scans a reservoir of a of photosensitive liquid along a predetermined path. Upon the laser beam being exposed to the portions of the liquid lying in the beam""s path, the exposed portions of the liquid cure or solidify through polymerization. An example of stereolithographic methods and equipment are disclosed in U.S. Pat. No. 5,256,340, which issued to Allison on Oct. 26, 1993 and which is assigned to 3D Systems, Inc.
Another known SFF process utilizes Cubital""s Solider system. In general, this process utilizes a photo-mask which represents the image of the particular layer of the object to be produced. The mask is positioned over a layer of photosensitive liquid. Selective solidification of the layer occurs upon exposure of ultraviolet light through the mask. Unsolidified resin is drained from the partially composed object leaving the desired configuration of surfaces and cavities. The cavities of the object are then filled with a liquid material having a relatively low melting point, such as wax. Upon solidification of the wax, the uppermost layer of the object is made uniform, such as by planing or milling. Then a new layer of the photocurable liquid is positioned on the surface. Another mask is created and the process is repeated. Upon completion of production, the wax is melted and pour from the object to expose the configuration of the object. As discussed below, the object may comprise a plurality of interconnected, internal cavities or may be hollow.
In addition to these specifically described SFF techniques, there are other techniques not described in detail here. Among these techniques are plasma deposition techniques whereby plasma is deposited along a predetermined path and permitted to solidify to build an object on a layer by layer basis. One such additive technique is known as Laser Engineered Net Shaping (LENS(trademark)) technology developed by Optomec, Inc., located in Albuquerque, N. Mex. The Optomec Directed Materials Deposition process uses a high power laser focused onto a substrate to melt the substrate surface. Metal powder is then blown into the melt pool to increase its volume. Subsequent scanning of the substrate relative to the laser beam provides a means to deposit thin metal lines on the substrate surface. With the addition of computer control, the Optomec system deposits the metal lines to form patterns on the substrate surface. Finally, this patterning method is coupled with the ability to interpret 3-D CAD designs and allows those patterns to represent a series of slices through the part from the CAD system. Using this method, a component can be fabricated directly from a CAD solid model one layer at a time until the entire object is realized. The result is fully dense metal parts with dimensional accuracy.
Solid Freeform Fabrication technologies depend on the use of computers to generate cross-sectional patterns representing the layers of the object being formed, and generally require the associated use of a computer and computer-aided design and manufacture (CAD/CAM) software. In general, these techniques rely on the provision of a digital representation of the object to be formed. The digital representation of the object is reduced or xe2x80x9cslicedxe2x80x9d to a series of cross-sectional layers which can be overlaid to form the object as a whole. The SLA or other apparatus for carrying out the fabrication of the object then utilizes the cross-sectional representations of the object for building the object on a layer-by-layer basis by, for example, determining the path of the laser beam in an SLA or the configuration of the mask to be used to selectively expose UV light to photosensitive liquids.
It is also known to form hollow structures wherein just the periphery or boundary skin of the object is formed. However, fabrication of entirely hollow objects sometimes is not acceptable because of limitations in the resultant structure and the photosensitive materials used by SLA. In particular, hollow structures fabricated by utilizing only a boundary skin often suffer from high structural stresses, shrinkage, curl in the materials and other distortions of the object.
It is also known to form the periphery of the object by formation of a substantially intact boundary skin, and to provide an integrally formed lattice located internally within the skin boundary. An example of such a technique or xe2x80x9cbuild stylexe2x80x9d is the QuickCast(trademark) system by 3D Systems, Inc. which can be used to produce three dimensional objects having a skin and a honeycomb-like internal structure or lattice extending between the boundaries defined by the skin.
The desired internal and external object geometry depends upon the anticipated usage of the object to be formed and is based upon a computer generated model or representation of the object. For example, it may be desirable to produce an object with a hollow portions, solid portions and portions occupied by a lattice work. These xe2x80x9cbuild stylesxe2x80x9d each have distinct advantages and disadvantages. For example, certain build styles, such as the QuickCast(trademark) build styles can be useful when the resultant object is to be filled with a material to solidify, strengthen or otherwise further process the object. The presence of a lattice build style can often afford more ready introduction of strengthening materials into the object, can provide dimensional stability, dimensional accuracy and functionality, or provide a more accurate model.
While it is thus generally known to use SFF processes utilizing a single lattice build style to make a three-dimensional object, such techniques and the resultant objects still have significant practical limitations. In particular, the materials used in some SFF techniques, such as photosensitive resins used in an SLA have physical characteristics which limit the usefulness of the resultant object. Among the features of the present invention is the enhancement of known SFF techniques to include multiple build style lattices in both the process of making the object and in the resultant object itself. In one embodiment, the invention provides an object that includes the structure of a first lattice build style which is integrally formed as a single piece. The object also includes a second lattice build style that is also integrally formed in a single piece and that is intertwined or interlaced with the structure of the first build style lattice. The respective structures of the first and second build style lattices are complementary and are sized and shaped to provide a resultant object having advantageous characteristics and utility.
In this regard, the multiple lattice build styles can be made in conjunction with a boundary skin layer to define the object being made. When multiple lattice build styles are constructed according to the present invention, advantageous results can be achieved that are unavailable using known SFF techniques. For example, interlaced lattice build styles can be used to form entirely solid objects as well as objects having solid regions and passages adjacent or extending through the solid regions. Such structures can be made either with or without a boundary skin on the object, and can provide passageways extending in close proximity to the boundary skin. By utilizing interlaced lattice build styles, objects having utility can be formed. For example, heat exchangers, gradient material components, stress relief structures and the like can be formed.
In one embodiment, the invention provides a three dimensional object including a first one-piece build style lattice including a plurality of substantially uniform build style units. The object also includes a second one-piece build style lattice integrally formed with and interlaced with the first lattice, the second lattice including a plurality of substantially uniform build style units. In another embodiment, the invention provides a method for forming a three dimensional object including the steps of: generating a digital representation of the object; generating a digital representation of a first build style lattice having a predetermined, substantially uniform structure; generating a digital representation of a second build style lattice having a structure similar to the first build style lattice; overlaying the respective representations of the object, the first build style lattice and the second build style lattice; intersecting the overlaid representations to generate a digital representation of the object incorporating the first build style lattice and the second build style lattice; and fabricating the digital representation of the object.
In another embodiment, the invention provides a three dimensional object formed through use of a free form fabrication method including the steps of: generating a digital representation of the object including a representation of a surface of the object; generating a digital representation of a first build style lattice having a predetermined, substantially uniform structure; generating a digital representation of a second build style lattice having a structure similar to the first build style lattice; intersecting the overlaid representations to generate a digital representation of the object incorporating the first and second build style lattices; and fabricating the digital representation of the object incorporating the first and second build style lattices to form a boundary skin, a first lattice integrally formed with and extending from the skin and a second lattice interlaced with the first lattice and integrally formed with and extending from the skin.